Induction hardening system and method

ABSTRACT

A system and method of induction heat treating a gear includes a workstation. The workstation has a power source, an inductor coil, and a rotational mechanism. The gear is induction heat treated at a first portion of the gear and a second portion of the gear remains untreated by induction hardening. The gear has an inner surface. The inner surface includes the first portion and the second portion. The first portion has a first width. The second portion has a second width. The inductor coil includes at least one heating loop and at least one non-heating loop. The inductor coil is energized to a predetermined frequency to create an alternating magnetic field, where the alternating magnetic field developed in the heating loop induces an eddy current in the first portion of the gear.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/322,771, filed on Apr. 9, 2010. The disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present invention relates to a system and method of hardening a gearor gear like object, and more particularly to a system and method ofselectively hardening a portion of an inner surface of the gear usinginduction heat treatment.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may or may not constitute priorart.

Gears can be hardened by an induction heat treatment to improve wearresistance. In one type of gear, the inner surface of the gear includesa plurality of splines. The splines do not cover the entirecircumference of the inner surface. Instead, the inner surface includesseveral webs, where a series of splines are located between each web.The webs are an area of decreased wall thickness along the inner surfaceof the gear. It is typically desirable to heat treat only the splines,as the webs have a reduced wall thickness that is susceptible to meltingor cracking.

In one approach, induction heat treatment is used to only harden thesplines. However, it is not possible to only heat treat the splines withthe current induction coil and process design technology. Anon-rotational induction heat treatment technique is employed, where thegear is oriented in a particular position and all of the splines areconcurrently heated by a coil placed within the inner surface of thegear. However, this non-rotational approach results in a non-uniform andunsymmetrical heat treat pattern, and also tends to overheat the webs,which leads to melting and cracking of the webs. As a result, severalsplines between each web will remain untreated in an effort to avoidoverheating the web. This results in gears that do not meet heattreatment specifications. The current approach of orienting the splinewith respect to the inductor coil requires special handling issues andadds to the cost of the product. Moreover, the current inductionhardening process also produces very deep hardening, or case, along theouter surface of the gear. Thus, the current approach of inductionhardening can produce that have built in stresses, which may lead topremature mechanical failure of the gears. As a result, there is a needin the art for a robust induction hardening process for a gear thatheats the splines uniformly without overheating the webs.

SUMMARY

The present invention provides a method and system for hardening a gearemploying a rotatable type induction hardening technique. A firstportion of the gear is induction heat treated and a second portion ofthe gear remains untreated. The gear has an inner surface. The innersurface includes the first portion and the second portion. The firstportion has a first width and the second portion has a second width.

The method includes a first step where the gear is placed within aworkstation. The workstation has a power source and an inductor coil.The power source provides alternating current to the inductor coil. Theinner surface of the gear is positioned to be proximate to the inductorcoil. The inductor coil includes at least one heating loop and at leastone non-heating loop. The heating loop has a heating loop width and thenon-heating loop has a non-heating loop width. The non-heating loopwidth is configured to be about equal to the second width of the gear.The heating loop width is configured be about equal to the first widthof the gear. In a second step, the gear is rotated about an axis ofrotation relative to the inductor coil. In a third step, the inductorcoil is energized to a predetermined frequency to create an alternatingmagnetic field. The magnetic field developed in the heating loop inducesan eddy current in the first portion of the gear. In a fourth step, theinductor coil is maintained at the predetermined frequency for apredetermined amount of time to induction harden the gear at the firstportion.

In another embodiment of the invention, the method comprises the step ofproviding a plurality of spline groups as the first portion of the gearand a plurality of webs as the second portion of the gear.

In an embodiment of the invention, the method comprises the step ofquenching the gear by fluid. Fluid is supplied to the gear by aquenching plate having a series of fluid passageways.

In another embodiment of the invention, the method comprises the step ofproviding a flux intensifier that is included within the quenchingplate.

In yet another embodiment of the invention, the method comprises thestep of positioning the inductor coil in place within the workstation bythe quenching plate. A portion of the inductor coil is located withinthe quenching plate.

In an embodiment of the invention, the method comprises the step ofrotating the gear about the axis at a rotary speed of about 1000 RPM.

In another embodiment of the invention, the method comprises the step oforienting the eddy current to extend lengthwise along the first portionof the gear.

In yet another embodiment of the invention, the method comprises thestep of orienting the eddy current to extend circumferentially aroundthe inner surface of the gear.

In an embodiment of the invention, the method comprises the stepproviding a portion of the non-heating loop that is parallel with theaxis of rotation of the gear.

In another embodiment of the invention, the method comprises the step ofcreating a net alternating magnetic field that is about zero in theportion of the non-heating loop that is parallel with the axis ofrotation.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1A is an exemplary illustration of a gear placed in a work stationfor carrying out an induction heat treatment;

FIG. 1B is a partial cross-sectional view of the gear of FIG. 1A showingthe propagation of an eddy current (EC) waveform through the innersurface of the gear;

FIG. 1C is an alternative embodiment illustrating the eddy current; and

FIG. 2 is an enlarged view of the gear illustrated in FIG. 1A.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Referring now to FIG. 1A, the reference numeral 10 designates anexemplary rotatable induction hardening work station having a powersource 20, an inductor coil 22, a quenching plate 24, a support member26 and a rotational mechanism 28. The support member 26 and thequenching plate 24 have been partially sectioned at a ninety degreeangle to show detail of a gear 30 that is hardened in the workstation10. The work station 10 is used to harden the gear 30 rotatablysupported by a spindle or rotation mechanism (not shown). In theembodiment as shown, the support member 26 is a phenolic block supporthaving a threaded aperture 31 and hose stem. The inductor coil 22 andthe quenching plate 24 are held stationary and surrounded by the gear30, which has an inner surface 32. The gear 30 is secured to therotational mechanism 28. The rotational mechanism 28 is any type devicecapable of rotating the gear 30 about an axis A-A such as, for example,a spindle. The gear 30 can be any type of rotating component used tomesh with another part in order to transmit torque. In one exemplaryembodiment, the gear 30 is either a drive or driven sprocket of atransmission. In the embodiment as shown, the work station 10 is used toharden the inner surface 32 of the gear 30. An outer surface 34 of thegear 30 includes a plurality of teeth 36 that are hardened using aseparate operation. In one example, the teeth 36 are hardened using asingle shot induction hardening process that is disclosed in U.S. Pat.No. 4,639,279, which is hereby incorporated by reference herein.

The inner surface 32 of the gear 30 includes a plurality of splines 42that cover a portion of the circumference of the inner surface 32. Thesplines 42 are arranged in a series of spline groups 44, where a web 46is included between the spline groups 44. The webs 46 represent an areaof reduced wall thickness along the inner surface 32 of the gear 30.Specifically, the spline groups 44 have a first wall thickness W1 andthe webs 46 have a second wall thickness W2, where the first wallthickness W1 is greater than the second wall thickness W2. Referring toboth FIGS. 1A and 2, the first wall thickness W1 is measured axiallyalong the inner surface 32 of gear 30, and represents the height of thespline groups 44. Specifically, the first wall thickness W1 representsthe distance between a top edge 35 and a bottom edge 37 of the innersurface 32. The second wall thickness W2 is also measured axially alonginner surface 32 of gear 30 and represents the distance between an edge51 of the web 46 and the bottom edge 37 of the inner surface 32. Theedge 51 of the web 46 represents a portion of an outermost boundary ofthe web 46 located nearest to the axis of rotation A-A of the gear 30. Aspline 50 can also be located below the web 46. The webs 46 represent anarea of reduced wall thickness and strength along the inner surface 32.Because of this, only the splines 42 are heat treated, as the webs 46have a reduced wall thickness are therefore susceptible to melting orcracking during heat treatment.

Referring to FIG. 1A, the inductor coil 22 is connected to the powersupply 20 through a pair of inductor leads 48. The power supply 20provides alternating current to the inductor coil 22. The inductor coil22 is energized by the power supply 20 to a predetermined frequency andpower level for a predetermined amount of time to achieve a desiredlevel of heating. The frequency, power level, and time are interrelatedand depend on the particular application and configuration of the gear30. Specifically, the inductor coil 22 produces an alternating magneticfield B that generates eddy currents within the gear 30 for inductionhardening. FIG. 1B illustrates a partial cross section of the gear 30with the splines 42 removed to illustrate the eddy currents EC extendinglengthwise along the inner surface 32 of the gear 30. The eddy currentsEC uniformly heat the splines 42. Alternatively, the eddy currents ECcan also extend circumferentially around the inner surface 32 of thegear 30 as well (as shown in FIG. 1C and labeled EC). The inductor coil22 is energized at the predetermined frequency for the predeterminedamount of time to achieve a desired induction heat treatment depth ofthe inner surface 32 of the gear 30.

Turning back to FIG. 1A, in the embodiment as shown the inductor coil 22is shaped in a predetermined configuration that depends on the innersurface 32 of the gear 30. The inductor coil 22 is shaped to include atleast one non-heating loop 52 and at least one heating loop 54, wherethe non-heating loop 52 has a width W3 and the heating loop 54 has awidth W4. The widths W3 and W4 of the non-heating loop 52 and theheating loop 54 can be adjusted to correspond to a particular gear 30depending on the configuration of the gear 30. Specifically, the widthW3 of the non-heating loop 52 is configured to be about equal to thewidth 64 of the non-splined portion measured around the inner surface 32of the gear 30 (shown in FIG. 2). The width W4 of the heating loop 54 isconfigured be about equal to the width 66 of the splined portion 44measured around the inner surface 32 of the gear 30 (also shown in FIG.2). The widths W3 and W4 of the non-heating and heating loops 52 and 54can be adjusted to match the dimensions of the splined and non-splinedportions of the inner surface 32.

The configuration of the non-heating and heating loops 52 and 54 createthe eddy current EC only in the splines 42 and 50 located along theinner surface 32 of the gear 30, while at the same time creating anegligible amount of eddy current EC in the webs 46. The orientation ofthe heating loop 54 creates the eddy current EC in the splines 42 and50. The orientation of the non-heating loop 52 causes the eddy currentEC to be cancelled in the regions along the inner surface 32 that arenot splined. Specifically, each non-heating loop 52 includes twogenerally opposing parallel portions 59 that are positioned parallel tothe axis of rotation A-A. The alternating magnetic field B travelingthrough one of the parallel portions 59 of one of the non-heating loops52 is in a direction that generally opposes the alternating magneticfield B traveling through the other one of the parallel portions 59 ofthe selected non-heating loop 52. The parallel portions 59 of eachnon-heating loop 52 are oriented in proximity to one other such that thealternating magnetic field B traveling through one of the parallelportions 59 of the non-heating loop 52 cancels the alternating magneticfield B traveling through the other parallel portion 59 of thenon-heating loop 52, resulting in a net alternating current that isnegligible or zero. This configuration of the non-heating loop 52creates dead spots with a minimal amount or no eddy current EC in thegear 30 where the webs 46 are situated. The webs 46 also represent aportion of the gear 30 with reduced mass and wall thickness, which alsocauses the eddy current EC to be minimal or non-existent where the webs46 are located. Also, the splines 42 and 50 of the gear 30 are situatedto be closer to the inductor coil 22 when compared to the webs 46 of thegear 30. Thus, only the splines 42 and 50 are heat treated, as a minimalamount or no eddy current EC is created in an area of the gear 30 thatdoes not include a spline. Therefore, only the splines 42 and not thewebs 46 of the gear 30 are heat treated. It is beneficial to onlyinduction heat the splines 42, as the webs 46 have a reduced wallthickness and are susceptible to melting or cracking during heattreatment.

The quenching plate 24 is used to position and secure the inductor coil22 in place within the work station 10, where a portion 58 of theinductor coil 22 is located within the quenching plate 24. The quenchingplate 24 includes a plurality of fluid passageways 60 that are in fluidcommunication with a fluid source (not shown). The fluid can be any kindof quenching fluid used to quench metallic materials such as, forexample, quenching oil or a water based polymer. The fluid passageways60 are used to communicate fluid from the fluid source to the innersurface 32 of the gear 30. Specifically, after the splines 42 have beenheated by the inductor coil 22, the inner surface 32 of the gear isquenched. Quenching produces a desired depth of hardening, or case,along the inner surface 32 the gear 30. Specifically, quenching the gear30 will produce case hardening to a predetermined heat treatment depth,thereby case hardening only the splines 42 and not the webs 46 locatedalong the inner surface 32 of the gear 30.

The quenching plate 24 can also include a flux intensifier formedtherein. The flux intensifier is employed to provide selective heatingto the splines 42 of the gear 30, improves the electrical efficiency ofthe inductor coil 22, and can also act as an electromagnetic shield toprevent the undesirable heating of the webs 46. The flux intensifier maybe constructed from a high permeability, low power loss material suchas, for example, a molded material including iron powders in anon-conductive binder.

The work station 10 is a rotatable type induction hardening device.Utilizing a rotatable type induction hardening device generallyeliminates the need to use an induction hardening technique where thegear 30 is oriented in a particular position within the work station 10.Requiring the gear 30 to be oriented in the induction hardening machinemay cause problems if the gear 30 is loaded into the induction hardeningmachine by a robotic device. Moreover, employing a rotatable typeinduction hardening device also reduces the instances of melting orcracking at the webs 46, can increase the gear's 30 dimensionaltolerances, and results in simpler and less expensive tooling. In oneembodiment, the gear 30 achieves improved hardness at the splines 42such that the gear 30 can potentially replace a more costly powder metalpart in a transmission.

With continued reference to FIGS. 1A-1C, a method of hardening a gear 30using the working station 10 is generally described. The method beginsby providing a gear 30 having the inner surface 32, the outer surface34, the splines 42, and the webs 46. The inner surface 32 of the gear 30includes a plurality of splines 42 that cover a portion of thecircumference of the inner surface 32, where the splines 42 are arrangedin a series of spline groups 44. The webs 46 represent an area ofreduced wall thickness and strength along the inner surface 32. Thespline groups 44 have a first wall thickness W1 and the webs 46 have asecond wall thickness W2, where the first wall thickness W1 is greaterthan the second wall thickness W2. Because of this, it is typicallydesirable to heat treat only the splines 42, as the webs 46 have areduced wall thickness and are therefore susceptible to melting orcracking. The method then proceeds to a second step.

In second step, the gear 30 is positioned within the work station 10such that the inductor coil 22 is surrounded by the inner surface 32 ofthe gear 30. The work station 10 is a rotatable type induction hardeningdevice, which means that the inductor coil 22 heats the splines 42 whilerotating the gear 30. The method may then proceed to a third step.

In the third step, the gear 30 is rotated by the rotational mechanism 28about the axis A-A relative to the inductor coil 22. In one exemplaryembodiment, the gear 30 is rotated at about 1000 revolutions per minute,however it is understood that other rotational speeds may be used aswell. Alternatively, the gear 30 may be oscillated relative to theinductor coil 22 as well. The method may then proceed to a fourth step.

In the fourth step, the inductor coil 22 is energized by the powersupply 20 to heat the splines 42 of the gear 30. The inductor coil 22 isenergized for the predetermined frequency and power level for apredetermined amount of time to achieve a desired level of heating. Thefrequency, power level, and time are interrelated and depend on theparticular application and configuration of the gear 30. Specifically,the inductor coil 22 produces an alternating magnetic field B thatgenerates eddy currents within the gear 30 for induction hardening.Referring to FIG. 1A an eddy current EC (FIGS. 1B-1C) generated withinthe gear 30 induction heat treats only the splines 42 and 50.Specifically, the heating loop 54 of the inductor coil 22 creates theeddy current EC that induction hardens the inner surface 32 of the gear30 only along the splines 42 and 51. Thus, the splines 42 but not thewebs 46 of the gear 30 receive the majority or greater amount of theeddy current EC flowing within the domain of the spline which is heatedby the inductor coil 22. The method may then proceed to a fifth step.

In the fifth step, the inductor coil 22 is maintained at thepredetermined frequency for a predetermined amount of time by supplyingpower to the power source 20. The method may then proceed to a sixthstep.

In the sixth step, the gear 30 is quenched by fluid communicated by aplurality of fluid passageways 60 located in the quenching plate 24.Quenching produces case hardening at a predetermined heat treatmentdepth, thereby case hardening only the splines 42 and not the webs 46located along the inner surface 32 of the gear 30. The method may thenterminate.

Induction hardening the splines 42 will produce a hardened outer surfacewhile still keeping the core of the gear 30 unhardened. This results inthe gear 30 having hardened surface properties while having a softer,more ductile core that provides toughness as well as enhances mechanicaland metallurgical properties. Induction hardening using the rotatabletype induction hardening approach reduces tooling costs as well, becausethe gear 30 does not need to be oriented in a particular position withinan induction hardening machine. Finally, induction hardening using therotatable induction approach will result in more uniform case hardeningdepths of the inner surface 32 of the gear 30, which results in improvedmechanical and metallurgical properties of the gear 30 when compared tothe current induction hardening techniques that are currently employed.

The description of the invention is merely exemplary in nature andvariations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A method of induction heat treating a first portion of a gear,wherein a second portion of the gear remains untreated by inductionheating, wherein the gear has an inner surface, wherein the firstportion and the second portion are located along the inner surface ofthe gear, and wherein the first portion has a first width and the secondportion has a second width, the method comprising: placing the gearwithin a workstation, wherein the workstation has a power source and aninductor coil, and wherein the inner surface of the gear is positionedto be proximate to the inductor coil, wherein the power source providesalternating current to the inductor coil, and wherein the inductor coilincludes at least one heating loop and at least one non-heating loop,where the heating loop has a heating loop width and the non-heating loophas a non-heating loop width, and wherein the non-heating loop width isconfigured to be about equal to the second width of the second portionof the gear, and wherein the heating loop width is configured to beabout equal to the first width of the first portion of the gear;rotating the gear about an axis of rotation, wherein the gear is rotatedrelative to the inductor coil; energizing the inductor coil to apredetermined frequency to create an alternating magnetic field, whereinthe magnetic field developed in the heating loop induces an eddy currentin the first portion of the gear; and maintaining the inductor coil atthe predetermined frequency for a predetermined amount of time toinduction harden the gear at the first portion.
 2. The method of claim 1comprising the step of providing a plurality of spline groups as thefirst portion of the gear and a plurality of webs as the second portionof the gear.
 3. The method of claim 1 comprising the step of quenchingthe gear by fluid, wherein fluid is supplied to the gear by a quenchingplate having a series of fluid passageways.
 4. The method of claim 3comprising the step of providing a flux intensifier that is includedwithin the quenching plate.
 5. The method of claim 3 comprising the stepof positioning the inductor coil in place within the workstation by thequenching plate, wherein a portion of the inductor coil is locatedwithin the quenching plate.
 6. The method of claim 1 comprising the stepof rotating the gear about the axis at a rotary speed of about 1000 RPM.7. The method of claim 1 comprising the step of orienting the eddycurrent to extend lengthwise along the first portion of the gear.
 8. Themethod of claim 1 comprising the step of orienting the eddy current toextend circumferentially around the inner surface of the gear.
 9. Themethod of claim 1 comprising the step of providing a portion of thenon-heating loop that is parallel with the axis of rotation of the gear.10. The method of claim 9 comprising the step of creating a netalternating magnetic field that is about zero in the portion of thenon-heating loop that is parallel with the axis of rotation.
 11. Aninduction heat treatment workstation for hardening a gear, wherein thegear has an inner surface, wherein the inner surface includes aplurality of splines that are induction heat treated and a plurality ofwebs that remain untreated by induction hardening, and wherein each ofthe plurality of splines have a first width and each of the plurality ofsplines have a second width, the workstation comprising: a power sourceproviding alternating current; an inductor coil where the power sourceprovides alternating current to the inductor coil wherein the innersurface of the gear is placed proximate to the inductor coil, andwherein the inductor coil includes at least one heating loop and atleast one non-heating loop where the heating loop has a heating loopwidth and the non-heating loop has a non-heating loop width, and whereinthe non-heating loop width is configured to be about equal to the secondwidth, and wherein the heating loop width is configured be about equalto the first width, and wherein the inductor coil is energized at apredetermined frequency to create an alternating magnetic field, whereinthe alternating magnetic field developed in the heating loop induces aneddy current in the plurality of splines of the gear to induction hardenthe gear at the plurality of splines; a rotational mechanism to rotatethe gear about an axis of rotation, wherein the gear rotates relative tothe inductor coil as the inductor coil is energized by the power source,and wherein the inductor coil is maintained at the predeterminedfrequency for a predetermined amount of time.
 12. The workstation ofclaim 11 comprising a quench plate, wherein the quench plate includes aplurality of fluid passageways that are in fluid communication with afluid source, and wherein the fluid passageways communicate fluid to theinner surface of the gear.
 13. The workstation of claim 12 wherein thequench plate positions and secures the inductor coil in place within theworkstation relative to the inner surface of the gear.
 14. Theworkstation of claim 12 wherein the quench plate includes a fluxintensifier formed therein.
 15. The workstation of claim 11 wherein aportion of the non-heating loop is parallel with the axis of rotation ofthe gear.
 16. The workstation of claim 15 wherein the alternatingmagnetic field in the portion of the non-heating loop that is parallelwith the axis of rotation is cancelled.
 17. The workstation of claim 11wherein the eddy current is oriented to extend lengthwise along theplurality of splines.
 18. The workstation of claim 11 wherein the eddycurrent is oriented to extend circumferentially around the inner surfaceof the gear.
 19. The workstation of claim 11 wherein the rotationalmechanism rotates the gear at a rotary speed of about 1000 RPM.
 20. Amethod of induction heat treating a gear, wherein the gear includes aninner surface, a plurality of splines and a plurality of webs, whereinthe plurality of splines and the plurality of webs are located along theinner surface, and wherein the plurality of splines are induction heattreated and the plurality of webs remain untreated by induction heating,and wherein each of the plurality of spline groups have a first widthand each of the plurality of webs have a second width, the methodcomprising: placing the gear within a workstation, wherein theworkstation has a power source and an inductor coil, and wherein theinner surface of the gear is positioned to be proximate to the inductorcoil, wherein the power source provides alternating current to theinductor coil, and wherein the inductor coil includes at least oneheating loop and at least one non-heating loop, where the heating loophas a heating loop width and the non-heating loop has a non-heating loopwidth, and wherein the non-heating loop width is configured to be aboutequal to the second width of the gear, and wherein the heating loopwidth is configured to be about equal to the first width of the gear;rotating the gear about an axis of rotation, wherein the gear is rotatedrelative to the inductor coil; energizing the inductor coil to apredetermined frequency to create an alternating magnetic field, whereinthe magnetic field developed in the heating loop induces an eddy currentin the plurality of splines of the gear, and wherein a net alternatingcurrent that is about zero is created in a portion of the non-heatingloop; and maintaining the inductor coil at the predetermined frequencyfor a predetermined amount of time to induction harden the gear at theplurality of splines; and quenching the gear by fluid, wherein fluid issupplied to the gear by a quenching plate having a series of fluidpassageways, and wherein a flux intensifier is included within thequenching plate, and wherein the inductor coil is positioned within theworkstation by the quenching plate and a portion of the inductor coil islocated within the quenching plate.